MSefi.com read only forum (Jan.15,2018)

[MSII, 3.0, v2.88, MT2.51, via Relay board]

I wanted to create a circuit on the Proto Area to use the Spare port for the Knock Sensor to control the +5V source required to an HEI distributor.
(I'm using the FIDLE to control Fans and am running an IAC & Ignition Control)

I've set up the circuit below on the Proto Area which as well as providing control over 'when' MS takes over Ignition control also lights up an LED when output is 0V (ie HEI module in control of Ignition during cranking)

I've run the +5V output to Spr4, Pin6 and with some previous mods to my relay cable and relay board (See Relay forum for MSII Mods) I've now pulled this controllable 5V source out into my wiring loom via the relay board.

I've seen a lot of questions on the forum re this subject so though I'd post a complete schematic of my modification.

James

Could someone please explain why you would want this?

The GM HEI distributor requires a +5V source into pin B.
If Pin B = 0V then the HEI module control timing (ie during cranking), when set at +5V the ignition contol passes over to Megasquirt.

There are a lot of ways to set this up, you can:
>Set a seperate relay up external to MS to switch from a 'hot on run but not crank' source to switch the TPS +5V source on/off.
> If your using the Relay box you can set the Fidle relay to do the same (if your not already using it) with a jumper to a 5V source and setting up the spare port options.
> You can (now) set pin B permanently at 5V from the TPS source and use MS to control Ignition during cranking (see MegaManual for set up options on this one).
> You can modify MS to use one of the three LED driver transistors in MS to act as a switch using a 5V pullup resistor.
> Or you can set up a seperate switch (as above) to do the same using another 'spare' output (ie Knock).

I chose to impliment the above as I am using the Fidle relay to drive fans, I didn't want to introduce a seperate relay to my loom and I wanted to use the HEI module rather than MS during cranking.

James